Understanding how the complex interconnectivity of the nervous system is established represents one of the major goals of developmental neurobiology. This project will use the Drosophila visual system as a model system to investigate the molecular mechanisms underlying axon target selection. The three sub-types of photoreceptor neurons (R cells) in each facet of the compound eye project along a shared pathway, but connect to neurons in different layers in the optic lobe. This sub-type specific axon targeting appears to involve differential gene expression. I will use a genetic screen based on visual behavior to identify genes expressed in sub-type specific patterns. Identified genes will then be assessed for their roles in R-cell subtype specification including sub-type identity, axon guidance and synaptic specificity. This should result in isolation of photoreceptor sub-type specific molecules including regulators of sub-type specific gene expression as well as axon guidance signaling molecules (eg., receptors) which determine the specificity of photoreceptor target selection.